Generally speaking, manuscripts and books dated earlier than 1840
will absorb water to an average of 80 percent of their original
weight. Some may absorb as much as 200% of their original
weight. Since there is a greater concentration of proteinaceous
material and receptivity to water in such early books and papers,
they are especially vulnerable to mold when damp. Modern books,
other than those with the most brittle paper, will absorb an
average of up to 60 percent of their original weight. Thus, in
estimating the original weight of a collection, if one assumes an
average of four pounds per book when dry for 20,000 books in each
category, drying techniques must be capable of removing approxi
mately 64,000 pounds of water from the earlier materials and
48,000 pounds from the latter.

The major part of all damage to bound volumes caused by swelling
from the effects of water will take place within the first four
hours or so after they have been immersed. Since the paper in
the text block and the cardboard cores of book bindings have a
greater capacity for swelling than the covering materials used
for the bindings, the text-block of a soaked book usually expands
so much that the spine assumes a concave shape and the fore-edge
a convex shape, thus forcing the text block to become partially
or completely detached from its binding. The board cores of
bindings absorb a great amount of water in such circumstances and
are usually the source of mold development between the board
papers and fly leaves. This is especially apparent when the area
in which water damage has occurred begins to dry out and the
relative humidity falls below 70%.

Although it is obviously important to remove as much moisture as
possible from the environment, it is essential that the water
content of the material be monitored because this will remain
dangerously high, long after the area is apparently safe .
Action taken to salvage the material should therefore be governed
by the water content of the material and not by the relative
humidity of the area. A water moisture meter, such as an Aqua
Boy can be used to measure the water content inside books and box
files. If such an instrument is unavailable a crude but quite
effective way is to use a mirror within but not touching the text
block. Condensation will cloud the mirror. A water content
measuring less that 7% is considered dry.

Leather and vellum books, especially those of the 15th, 16th, and
17th centuries, can usually be restored successfully if they are
dried under very carefully controlled procedures. Such materials
are usually classified as rare and should be treated accordingly
by not mixing them with less rare materials during preparations
for salvage, stabilization and drying. The advice of a certified
book conservator may be essential in order to safely carry out
the most appropriate methods. If the material is frozen, freezer
paper should be used between each volume to prevent sticking.
(Refer to the section on freeze-drying for the special require
ments needed for drying this type of material).

Unfortunately, modern manufacturing processes so degrade the
natural structure of leather that, once water soaked, book covers
are often impossible to restore. Some leather bindings will be
reduced to a brown sludge, while others will severely shrink.
Swelling of covering materials, such as cloth, buckram, and
certain plastics is negligible, in some cases shrinkage occurs.
Book covers, however, which are made of a highly absorbent
cardboard, will absorb water to a greater degree than an equiva
lent thickness of text block. Some book covering materials which
have already deteriorated will absorb water at about the same
rate as the text block.

Once access to the collection is gained, the external appearance
of each volume and group of volumes is a useful indication of the
degree of water damage. Those volumes found, usually in heaps,
in the aisles will naturally be the most damaged. Not only will
they have sustained the shock of falling, as rapid swelling
caused them to burst from the shelves, but they will also have
been exposed to water for a longer period than the volumes on the
shelves above them. These will need special, flat packing and
the most extensive restoration. The appearance of such volumes
can be a devastating, emotional experience, but one must not
panic since every volume worth the cost of salvage and restora
tion can be saved.

Above the floor levels there will be distinct signs among the
shelves of the locations of the wettest material. Shelves which
have expanded under the pressure of swollen paper and bindings
will usually contain a mixture of evenly wet as well as unevenly
wet material. The proportion of evenly wet material in these
situations is usually less than those that are unevenly wet.
This is because books, originally shelved closely packed together,
will not easily be completely saturated especially if the
paper is slow to absorb. This is the major reason why so many
books become misshapen and distorted after water damage and also
after they have been frozen and dried. If paper is unevenly wet,
it will not dry without distortion. Misshapen volumes with
concave spines and convex fore-edges can be immediately identified
as belonging to the category of very wet. Others that have
severely swollen text blocks but that still retain some spine and
fore-edge shape may indicate that they were previously bound with
library binding oversewing techniques and may have sustained
irreversible sewing structure damage. Others may be relatively
sound in shape and these stand the best chance of drying with the
minimum of distortion.